In general, a torque motor is an electromechanical device having a body, an armature, polepieces terminating in poles, a permanent magnet, and at least one coil. Torque motors have various uses, such as in the pilot-stage of an electrohydraulic servo-valve.
As representatively shown in U.S. Pat. No. 3,023,782, a conventional torque motor has upper and lower polepieces terminating in two pairs of poles, with the opposing poles of either pair being arranged in spaced facing relation to one another. An intermediately-pivoted T-shaped armature is mounted on the body, and has its left and right marginal end portions arranged between the pairs of facing poles to define four variable-reluctance air gaps between the armature and these various poles. The aggregate length of the air gaps in any such cooperative adjacent pair is a constant, with the individual lengths of the respective gaps of any adjacent pair between opposed poles varying in a reciprocal manner (i.e., as one increases in length, the length of its cooperative mate decreases, and vice versa). These air gaps may also be thought of as being arranged in cooperative diagonal pairs such that as the length of one air gap in a diagonal pair increases or decreases (as appropriate), its reciprocal diagonal pair mate will also increase or decrease by the same amount.
A permanent magnet(s) is operatively arranged to create flux in each of the air gaps. The magnitude of the magnet flux (i.e., the flux attributable to the magnet) in any given air gap is a function of the length of that particular gap. Coils surround the marginal end portions of the armature, and are adapted to be selectively energized to create a coil flux (i.e., a flux attributable to the coils) in the various air gaps. The coil flux is superimposed on the magnet flux already present in the air gaps. The total flux in each air gap is, therefore, the algebraic sum of the magnet flux and the coil flux. If the coils are energized with a current of one polarity, the coil flux will be additive with respect to the magnet flux such that the total flux in a particular air gap will be the sum of the magnet and coil fluxes. On the other hand, if the coils are energized with currents of the opposite polarity, the coil flux will oppose and buck the magnet flux in such air gap, and the total flux in such air gap will be the difference therebetween.
The force of attraction between the armature and a pole is inversely related to the length of the air gap therebetween. As the length of such air gap decreases (i.e., as by a proximate portion of the armature moving toward the associated pole), the force of attraction increases. Conversely, as the length of an air gap increases (as by such proximate portion moving away from the associated pole), the force of attraction decreases. Because of this, torque motors are particularly suitable for bistable toggle-like applications where the armature latches against one pole or another. Hence, in a conventional latching-type torque motor, a desired current of one electrical polarity can be momentarily supplied to the coil to selectively move the armature to a hard-over or latched position. Thereafter, the coil can be de-energized, and the armature will remain in such latched position. To move the armature to its opposite position, the coil is energized with a current of opposite electrical polarity. This then causes the armature to pivot from one hard-over position to its opposite hard-over position. After the armature has been moved to this alternative position, the coil can be de-energized, and the armature will remain latched in this alternative position.
It is also known to provide a centering spring that urges the armature to move to a centered position between the poles in the absence of a supplied coil current. In the aforesaid '782 patent, this centering spring was provided by means of a flexure tube. (See, e.g., '782 pat., col. 6, line 42 et seq.) Other types of torque motors are representatively shown and described in U.S. Pat. Nos. 2,767,689, 3,455,330, 3,542,051 and 4,641,072. The aggregate disclosures of each of the aforesaid patents are hereby incorporated by reference insofar as the structure and operation of these various prior art torque motors is concerned.
In recent years, certain manufacturing techniques have been developed in micro electrical mechanical systems (“MEMS”). These techniques apply semiconductor batch-fabrication techniques to produce multiple photomask-defined acid-etched electronic devices on a silicon wafer substrate. Thus, MEMS manufacturing processes enable the fabrication of micro electrical mechanical devices, such as sensors and actuators, in large quantities and at low cost. See, e.g., Petersen, “Silicon as a Mechanical Material”, Proceedings of the IEEE, Vol. 70, No. 5 (May 1995), and Angell, Terry & Barth, “Silicon Micromechanical Devices”, Scientific American (April 1983). Hence, whereas conventional torque motors have heretofore been manufactured in large size or macro scale by conventional machining and formulation techniques, it is believed that the developments in MEMS technologies now enables a torque motor to be built on a miniaturized or micro-sized scale.
The desire to produce micro-sized torque motors is now further enhanced by a desire to produce miniaturized components, such as propulsion system for maneuverable satellites and other space vehicles. In addition, it is thought that the application of MEMS technology may allow a large number of parts and components to be manufactured smaller, at higher precision and less expensively than possible with macro-sized devices using conventional machining practices.